Bracket engine, what would you build and why?
You got a built 904 I can buy cheaper than the adapter?
I think going back to a 3sp, at the expeced weight of a B wedge with some alimunum will really mess with your suspension tuning and it will be slower even when you eventually get it to work. Your choice - but I'd leave the 'glide.
Here's a "for instance" on a B stroker:
383 + .030
full block machining but stock caps and main studs
pump gas (91 w/10% ethanol)
Stealths - Level 3 hand ported
Muscle Motors 4.25 stroker kit (4.25 x 4.280 bore is 496")
modified stock wet sump oiling w/stock pan & windage tray
port-matched RPM dual plane
custom Comp solid flat tappet, under .530 lift, under 244° @ .050, 1.5 rockers
belt driven water pump & p/s pump
Factory exhaust manifolds, 2.5" modified stock type full exhaust
Stock factory air cleaner (car won 1st in Stock Appearing at Carlise)
This is a low maintenance, pump gas engine, running street type carb, intake, and exhaust. It's made about 430hp to the tires, 450tq. Depending on your math that's around 510-520hp.
With .070 more bore, a real cam, race intake, and race headers I would imagine another 50-80hp is easy to get on the same fuel without exotic oiling, vacuum pump, or alcohol. It's barely touching it's potential as it was built as stock appearing and all street duty. The 383 is not my first choice for block - the 400 would be stronger.